Birmingham's progress in school attainment risks being put into reverse under proposals in yesterday's Education Bill, a union leader says.
Brian Carter, West Midlands regional secretary of the National Union of Teachers, claimed allowing schools to "go their own way" in independent trusts was a mistake.
He said the drive to greater autonomy along with academies would demolish the foundation of decades of educational success in the city.
"In Birmingham, the danger of trust schools with city academies could accelerate the breaking up of what has been a very helpful ethos in the city as a result of boosting morale of teachers and students," he said.
"With the creation of academies and trust schools there will be a temptation to go their own way. The council will have no formal control. It is a stark future for Birmingham if this Bill is successful."
Writing in The Birmingham Post today, Education Secretary Ruth Kelly applauds Birmingham's success in boosting pupils getting at least five good GCSEs from a third in 1997 to 56 per cent last year.
Mr Carter claimed achievement was a result of the strong local authority leadership the Education Bill would undermine.
"The philosophical concern is the move to outsource every service," he said. "Where schools are run in an entrepreneurial way you don't get the benefit of scale local authority provided services give.
"I don't think we should be demoting LEAs to a strategic role. Schools need a lot of support. What we will see is popular schools building larger schools while others go to the wall and we will see a lack of co-ordination, co-operation and collaboration between schools out for themselves."
Mr Carter said trust schools were a solution to a "London problem" "pummelled" across the country.
"London has a lot of little LEAs," he said. "Birmingham is the largest education authority in the country and is a cohesive authority with an successful community emphasis."
Trust schools are a key plank of the Bill, a crucial part of Labour's reforms.
The Government believes giving schools the power to innovate, free from local authority control and backed by private organisations and parents, gives greater choice and is the best way to combat failure.